CLEVELAND, United States (AFP) — Donald Trump’s presidential campaign came under withering scrutiny yesterday, after a nightmare start to the Republican convention capped by an embarrassing plagiarism scandal that tarnished his wife Melania’s prime-time speech.

After an opening day in Cleveland that was marred by a vocal and very public rank-and-file revolt by anti-Trump delegates, Melania’s address was meant to get the show back on track.

The conventions are designed to champion the party candidate, rally the grassroots and propel the party toward November’s election.

With millions watching on television, the Slovenian-born former model delivered an eloquent and seemingly heartfelt defensce of her husband.

“Donald is and always has been an amazing leader,” said the 46-year-old. “Now, he will go to work for you.”

But there were unmistakable similarities between her remarks and a speech given by Michelle Obama at the 2008 Democratic convention.

While the controversy burned for 12 hours and social media erupted with mocking commentary, the Trump campaign appeared paralysed.

Denials of wrongdoing, followed by tacit admissions, followed by attempts to insulate Melania only added to the picture of a campaign in chaos.

Campaign chair Paul Manafort described the whole kerfuffle as “absurd”, and Trump’s supporters seemed unperturbed.

“There’s just a passion for Donald, and his wife knocked it out of the park,” said Robert Antonacci of the New York delegation.

“Who cares? It was her speech. I don’t believe for a minute that Melania and Donald were sitting around going, ‘Hey, let’s plagiarise Michelle Obama’s speech.”’

‘Very proud’ Trump

Trump himself was ultimately forced to come out in his wife’s defence.

“It was truly an honor to introduce my wife, Melania. Her speech and demeanour were absolutely incredible. Very proud!” he tweeted.

Earlier, making a surprise cameo appearance at the gathering in Cleveland to introduce his wife, the bombastic tycoon showed confidence that belied the day’s drama.

“We’re going to win so big” said Trump. “Ladies and gentlemen, it is my great honour to present the next first lady of the United States.”

Republican establishment figures — whose party was once respected for its discipline and public unity — are now suggesting the speechwriter be fired and defending Trump as a candidate.

“The distraction gets you off message a little,” said Republican party boss Reince Priebus, though he added that he expected the flap to fade quickly.